This invention relates to a ceramic capacitor having a dielectric body containing a major proportion of a lead lanthanum zirconate titanate and a minor proportion of barium titanate.
Lead lanthanum zirconate titanate (PLZT) formulations having a strong antiferroelectric characteristic variously doped with silver and bismuth are shown to be exceptionally useful capacitor dielectric materials in my U.S. Pat. No. 4,027,209 issued May 31, 1977, and in my patent application Ser. No. 802,160 filed May 31, 1977, both being assigned to the same assignee as is the present invention. These materials have a high dielectric constant (K) that is relatively stable as a function of temperature and of the magnitude of voltage stress. Many if not most capacitors today are employed in circuits wherein the capacitor is stressed to about 100 volts or less. Monolithic ceramic capacitors normally employ dielectric ceramic layers of about 1 mil (0.001 inch or 0.0025 cm) thick so that 100 volts applied to the capacitor causes about 100 volts/mil stress in the dielectric. The above noted silver doped PLZT materials are generally more stable at 100 volts/mil than required for most uses.
It is therefore an object of the present invention to provide a capacitor having a temperature stable PLZT dielectric exhibiting antiferroelectric properties and an enhanced dielectric constant.
It is a further object of this invention to provide a ceramic capacitor, wherein the ceramic has a high dielectric constant at from 0 to about 100 volts/mil stress.